An electrographic image forming apparatus includes an optical scanning device emitting scanning light. The optical scanning device irradiates a surface of a photoreceptor by the scanning light to form an electrostatic latent image corresponding with image data.
For example, an image forming apparatus includes a base of the optical scanning device, two positioning pins press-fitted into the base and inserted into holes of a device body, and pressing members pressing the respective positioning pins from a radial direction (refer to Patent Document 1). If each pressing member is fastened by a screw, each positioning pin is fixed in a pressed state. That is, the base is positioned to the device body via each positioning pin. Subsequently, the optical scanning device is fastened to the positioned base with a plurality of screws.